THIS invention relates to a power generating device. More specifically, the invention relates to a renewable energy power generating device for converting wind and/or water-flow energy into useable electrical power.
Renewable energy power generating devices are well known, with most known devices typically converting wind and/or water-flow energy into reciprocating or rotary mechanical energy for driving some form of generator for producing electrical power.
Although this present invention may be configured to produce a reciprocating motion for driving a generator, a rotary-type motion is preferable in that such motion is smooth, continuous and, at least for extended periods, moving in a single direction.
When the concepts of wind powered devices (i.e. turbines) and/or water powered devices (i.e. waterwheels) were first being explored, most such devices incorporated blades with relatively large surface areas to capture passing wind or water-flow thereby to drive the blade in the direction of flow and power the turbine.
The disadvantage of such devices is that the blades do not provide drive continuously throughout the cycle. Typically, the cycle is broken substantially into a drive phase, where the blades are driven in the direction of flow, and a return phase, where the blades move against the flow to return to the start of the drive phase.
During the return phase of the cycle, the blades moving against the flow create drag, significantly reducing the efficiency of these devices. Many attempts have been made to address the disadvantage of drag created during the return phase. One such attempt is by pivoting the blade during the return phase into a condition offering less drag. Another attempt, and one that is of far more interest in respect of the present invention, is by replacing the large surface area resistive blades with wing-type blades (i.e. aerofoil or hydrofoil blades), which generate drive as a result of creating lift.
Most of the known wing-type turbine or waterwheel devices, for example the one taught by Monagahn in international patent application no. PCT/AU2011/000793 (published as no. WO 2012/000025), incorporate a plurality of symmetrical section aerofoil blades pivotally connected to a waterwheel structure having systems to pivotally control their respective angles of attack throughout rotation of the waterwheel thereby to orientate the blades correctly relative to the direction of flow to produce lift.
Typically, these control systems drive pivotal movement of the aerofoil blades about their respective pivot axis on the waterwheel by internal drive mechanisms (i.e. gearing between the blade and the pivot axis), or alternatively by making use of external ailerons at leading and/or trailing edges of the blades.
There are however at least two significant shortcomings in respect of these known wing-type turbine or waterwheel devices. Firstly, the control systems (particularly the external type) are overly complicated and exposed to damaging forces and corrosive elements especially in high current deep-sea applications.
Secondly, to enable lift to be generated throughout the cycle, the use of symmetrical section aerofoil blades at first glance appears to be the obvious solution. However, symmetrical section aerofoil sections, as opposed to non-symmetrical lift generating aerofoil sections, do not offer optimum lift characteristics.
As such, to address the shortcomings of the prior art, there is a need for a turbine/waterwheel type device having non-symmetrical lift generating aerofoil section blades. However, such blades must be configurable in such a manner to produce lift substantially throughout the rotational cycle. It is envisaged that this may be attainable by incorporating either an inverting fixed profile non-symmetrical aerofoil section blade, or a reversible variable camber aerofoil section blade, the latter being the preferable option.
Furthermore, incorporation of a reflexed camber into either of the abovementioned fixed or variable profile non-symmetrical aerofoil section blades will enable the blades to automatically orientate to the optimum angle of attack without having to pivotally drive the blades into the required position. In so doing, it is envisaged that the control systems required will be simple and housed substantially within the aerofoil blade, thereby protecting the control system from external damaging forces.
For background purposes, the camber of an aerofoil or wing can be defined by a mean camber line, which is the curve or line that is somewhat between the upper and lower surfaces of the aerofoil and passing through the aerofoil's leading and trailing edges, that is, the forward most and rear most points of the wing respectively. An aerofoil where the camber line reverses curvature direction near the trailing edge is called a reflexed camber aerofoil.
Reflex aerofoils are the type of section used in flying wing aircraft due to the inherent tendency of the shape to induce a rotational moment to the trailing edge of the wing, so as to replace the more traditional tail plane surface that is used to maintain the wing at a stable positive angle of attack. This wing section, when used in a flying wing or blended wing/fuselage configuration, has considerable advantages in aircraft design where the omission of the tail boom and tail plane reduces drag by a large factor. The advantages offered by reflexed camber aerofoil sections in aircraft applications are clearly transposable to turbine type applications.
It will be appreciated that the preferred embodiment of the aerofoil blade that forms part of the present invention is functionally the same or similar to the wing invention described in the inventor's previously filed international patent application no. PCT/ZA2013/000090 (published as no. WO 2014/085835), fully incorporated hereinto by reference.
It will be appreciated further that reference to the term aerofoil will be understood to include any lift generating member such as wings, hydrofoils, etc.